SALT LAKE CITY (AP), Jul 26 - A mystery man believed to be his 70s has been locked up in a Utah jail for more than three weeks and has baffled investigators because he refuses to reveal his identity or provide any details about his life.

The graying, disheveled man with blue eyes and a scruffy face was booked into the Utah County Jail as ``John Doe'' after being arrested for trespassing in the Provo Police Department parking garage.

Since then, investigators have been publicizing his mug shot and reaching out to the media and public to figure out who he is. About 100 tips have led nowhere.

``He's here on some misdemeanors but the fact is, we still don't know who he is. He could be wanted in another state. He could just be a missing person,'' said Lt. Dennis Harris of the Utah County Sheriff's Office. ``For some reason, he just plain flat doesn't want us to know who he is.''

Harris said the man was arrested July 1 in the underground police parking garage, about 45 miles (70 kilometers) south of Salt Lake City. He said an officer spotted the man peering into city vehicles. The man was asked to leave several times but refused and was arrested.

The man faces three misdemeanor charges of interfering with an investigation, failure to provide information to a police officer and criminal trespass. He's been ordered held on $1,200 cash bond.

He had no wallet when arrested, and Harris doesn't think the man can pay his bond.

Meantime, the man sits in jail, practically silent, save for a few brief conversations with Harris and a deputy who have been trying to get him to talk. Authorities ran the man's fingerprints through a state database but came up with nothing. They planned to submit them to an FBI database Tuesday.

``The only thing that I can even elicit from him is he said that at some point in time, he would need to get out,'' Harris said. ``That's the only thing he's given us. Whatever that means, I don't know.''

Harris said he has tried to get the man talking about family, his past - anything at all - but he reveals nothing.

``Sometimes he'll bring a smile to his face, but he's not giving us any indication of who he possibly could be,'' Harris said. ``The guy appears to be fairly smart. He is kind and polite.''

Harris said authorities don't believe the man is from Utah or has been homeless long, if he is homeless at all. The man has just about a week's worth of facial hair but did appear disheveled and dirty when he was arrested.